PHOTOELECTRON-SPECTRA OF PYROMELLITIC DIANHYDRIDE, DITHIOANHYDRIDE AND DIIMIDE AND OF TRIMELLITIC ANHYDRIDE

The photoelectron (He(I)) spectra of the tricyclic tetracarbonyl compounds pyromellitic dianhydride, dithioanhydride and diimide and of the tetracyclic hexacarbonyl compound trimellitic anhydride have been investigated. To aid the interpretation of the main features of the spectra, i.e. the ordering and splitting of the nCO ionisations and the behaviour of the 'benzenic' and heteroatom π ionisations, MO calculations based on a ZDO pragmatic model and semiempirical SCF-PP calculations have been carried out. The evolution of the nCO and πX ionisations upon progressive fusion of anhydride moieties with a benzene nucleus is analysed in detail. The proposed orbital sequences for the n orbitals are: ag(S+) $ ̌b1u(AS+) $ ̌b2u(S-) $ ̌b3g(AS-) for the tetracarbonyls and a′1(S+) $ ̌e′(AS+) $ ̌a′2 (AS-) ≈ e′(S-) for the hexacarbonyl. © 1979.